Select the latest available version of R to install. As of 2020-08-17 the latest version was R-4.0.2.pkg.
Click on the link for the latest version to download the most current version of R.
Complete the installation process as demonstrated in the following video.
Go to https://rstudio.com/products/rstudio/download/#download.
RStudio will recommend the latest version for your operating system at the top of your web browser with a blue download button. Click this button to download RStudio.
Complete the installation process as demonstrated in the following video.